1. Technical Field
The present invention relates to a piezoelectric gyro element for detecting angular velocities of directions of two axes, and a piezoelectric gyroscope that uses the element.
2. Related Art
Piezoelectric gyroscopes are commonly and widely used as orientation controls or as navigation systems for vessels, aircrafts, and automobiles, etc.; angular velocity sensors for image stabilizers and stability detection or the like in video cameras, etc.; and rotation direction sensors of a three dimensional mouse, etc. Many of the common piezoelectric gyro sensors is structured so as to detect the angular velocity of a rotation within one plane, or in other words, an angular velocity in the direction of one axis. In order to detect angular velocities of the directions of two axes, it has been necessary so far to use two piezoelectric gyro sensors and arrange them orthogonally to each other.
Hence, various structures of piezoelectric gyro sensors, which can detect the angular velocities of the direction of two axes with single piezoelectric gyro sensors, are being developed and suggested. For example, a vibratory gyro, which has a cross-shaped vibratory elastic body that has two axes intercrossing at a right angle, and is provided with a oscillator that excites vibratory elastic body in a flexure vibration mode so that the phases in the direction of the two axes will be opposite to each other, is known. JP-A-8-271256 is a first example of this related art. In vibratory gyros with such structure, the size of the entire device grows larger, and the cost increases.
An angular velocity sensor, which can simultaneously detect two angular velocities with a single sensor in a simple structure, by fixing one end of the vibration material for vibration detection and making the other end rotate in a circular path, is also suggested. JP-A-7-92175 is a second example of the related art. This angular velocity sensor has a pair of piezoelectric bodies and a pair of electrodes that are respectively adhered on each side face of the flexible, columnar vibration material. The free end of the sensor's vibration material performs a rotation (a circular motion), by being oscillated with driving output signals that are 90 degrees apart from each other phase-wise. The angular velocities are detected by utilizing the Coriolis force generated by an external force that is activated during the motion.
However, in the angular velocity sensor as described in the second example of related art, it is not the vibration material itself that shrinks and expands, but the sheet piezoelectric body adhered on its side face, and thereby the vibration material oscillates. This involves a problem that oscillation loss may occur depending on the adhesive status of the piezoelectric body, resulting in a decline in drive efficiency. Moreover, if the oscillation takes place in a high frequency, the piezoelectric body may flake off the surface of the vibration material, causing the detection sensitivity to drop significantly, or possibly to be lost entirely. These problems can be eliminated by altering the vibration material with a piezoelectric material. However, taking into account the structure of the driving electrode in common angular velocity sensors, it is not possible to make vibration material made of piezoelectric material rotate in a circular path, in a mechanism similar to the one described above.